Reflecting the event’s entertainment theme, there were men running in tutus, a man in a Speedo, women wearing tiaras, barefoot runners, men dribbling basketballs.

Never missing a photo-op, Mayor Bob Filner grabbed a blow-up guitar and posed with the Elvis impersonators.

“I am the king,” cried Filner.

Not on this day. That honor belonged to Koech and the half marathon.

While the event has included a marathon every year since its 1998 inception, the half marathon has become the emphasis.

Sunday’s starters: 18,106 in the half marathon, 6,566 in the full.

Professionally, the Rock ’n’ Roll organizers created a six-race, worldwide half marathon series that will pay nearly $500,000 in prize money.

Matt Turnbull, who recruits the pro athletes, lined up three men with sub-1-hour personal records.

Add a new, fast course featuring some screaming downhills and the ingredients were perfect for Koech’s performance.

“But this fast?” posed Turnbull.

Here were Koech’s mile splits through six miles: 4:25, 4:33, 4:26, 4:28, 4:29 and 4:23. After dusting the field, Koech said he had no idea the course was clock friendly.

When did it sink in?

“At the 10K,” he said.

His time through 6.2 miles: 27 minutes, 48 seconds. Some perspective: while Koech would be covering 13.1 miles, his 10K time ranked as the eighth fastest in the world this year.

By then, Koech had separated himself from the field, including Kipchoge, a two-time Olympic bronze medalist in the 5,000

“When you’re running by yourself,” Koech said, “it’s very hard. I just tried to push.”

While Koech’s half marathon was historic, it will not be recognized as a record. By USA Track & Field standards, for a course to be record certified it cannot descend more than one meter per kilometer.

From Balboa Park to Petco, the course dropped from 325 feet elevation to 25 feet, more than four times the permissible level.

“I don’t care about any descent,” said Meb Keflezighi, who finished fourth after winning the half marathon the past two years. “That’s the fastest half marathon ever run in the United States. Major, major credit to him.”